A liquid crystal display (hereafter “LCD”) is a known device used to control the transmission of polarized light energy. The LCD may be either clear or opaque depending on the current applied to the LCD. Because of this functionality, projection system commonly use an array containing numerous LCDs to form an image source. In particular, the projection system inputs high intensity polarized light energy to the LCD array (also called an imager), which selectively transmits some of the inputted light energy to form a projection of a desired image. Because a single LCD is relatively small, numerous LCDs can be packed together into the array, thereby forming an imager that can produce a high resolution image.
As suggested above, a projection system must first polarize the light input to the LCD. However, light energy from a light source, such as a bulb, may have either p-polarization or s-polarization. Since this light input to the LCD imager must be in one orientation (i.e., either p-polarization or s-polarization), the LCD projector generally uses only half of the light energy from the light source. However, it is desirable in projection systems to maximize the brightness and intensity of the light output. In response, various methodologies have been developed to capture the light energy of unusable polarization, to convert the polarization of this captured light energy, and then to redirect the converted light energy toward the LD imager. These known polarization recovery methodologies involve creating an expanded beam of light in which the unused portion of the light (of undesired polarity) is sent through a half-wave plate to change the polarization and then recombined with the original polarized beam. Unfortunately, the implementation of these known methodologies requires complex, bulky systems, which usually include 2-dimensional lens arrays and an array of polarization beam splitters. Furthermore, the known methodologies lose much of the light energy and, therefore, compromise the projector's goal of producing a high intensity output.
Light pipe systems have been used to separate white light into their individual red (R), blue (B), and green (G) components using light pipes, prisms, and beam splitters. The reverse of such a system can be used in combining multiple light sources with distinct spectrum without increase in etendue. Therefore, it is desirable to have a system the provides multi-colored illumination without the need to increase etendue.